1. Field of the Invention
The present invention relates to a surface inspecting apparatus for inspecting a surface of an object to be inspected, for example a body panel constituting a body for a vehicle. More particularly, the present invention relates to a surface inspecting apparatus which is capable of inspecting the existence of surface defects such as irregularities on a surface of the body panel subjected to a press working.
2. Description of the Related Art
Japanese Unexamined Patent Publication (kokai) No. 8-5573 shows conventional surface inspecting apparatus. The surface inspecting apparatus disclosed in this publication is provided with an illuminating unit as a light source, for emitting light in the form of a plane to a surface of a workpiece as the object to be inspected. In arrangement, the illuminating unit is obliquely positioned upward one side of the workpiece. The apparatus further includes an area sensing camera as an imaging unit, which is obliquely positioned upward the other side of the workpiece, for capturing the reflected plane light to take a picture of the surface of the workpiece. In this way, alien substances and projections existing on the surface of the workpiece are detected by the above surface inspecting apparatus.
This publication also discloses another type of surface inspecting apparatus. This surface inspecting apparatus includes an illuminating unit for emitting light in the form of a line to the surface of the workpiece. In arrangement, the illuminating unit is obliquely positioned upward one side of the workpiece, too. Similarly to the previously-mentioned apparatus, the surface inspecting apparatus further includes a line sensing camera as the imaging unit, which is obliquely positioned upward the other side of the workpiece, for capturing the reflected linear light to take a picture of the surface of the workpiece. In this way, micro-projections etc. existing on the surface of the workpiece are detected by the surface inspecting apparatus. Note, in this specification, the illuminating unit for emitting light in the form of a line may be also referred as "linear light source".
In common with the above-mentioned surface inspecting apparatuses of different types, an incident angle .alpha. of the illumination light from each light source and a reflecting angle .beta. of the reflected light captured by each sensing camera are both included within a range from 80 to 90 degrees, being generally equal to each other. That is, both of the surface detecting apparatuses are adapted so as to capture the so-called regular reflection light (alias, specular reflection light) for a captured image. In this case, the alien substances and defects on the surface of the workpiece are imaged as various shadows, in detail, dark spots in a bright zone on a display.
As a reference, it is noted that Japanese Unexamined Patent Publication (kokai) No. 6-3286 discloses a large and complex surface inspecting apparatus with an "inverse" reflecting screen, which utilizes oil to be applied to the surface, for equalizing the gloss of surface thereby detecting the surface defects stably.